This invention relates to a urea derivative and a method for colorimetric determination of an oxidizing substance or a peroxidase-like substance using said urea derivative as a chromogen.
Measurement of living body components, for example, body fluid components such as blood, urine, etc., is essential for the diagnosis of diseases, the elucidation of the state of diseases and course of remedy, since the change or the amount in the living body components is largely related to the diseases. Thus, there have been developed many methods for measuring various kinds of trace components such as cholesterol, triglyceride, glucose, uric acid, phospholipids, bile acids, monoamine oxidase, and the like in blood. It is well known that these methods are useful for the diagnosis of diseases.
As methods for measuring serum components, there are widely employed in general so-called "enzymatic methods" comprising using an enzyme which acts on the desired component specifically when the desired component is other than enzymes, or using a substrate compound when the desired component is an enzyme, conducting an enzymatic reaction respectively, and measuring the product to obtain the amount of the desired component. Among these methods, with the development of oxidizable color producing reagents, there is employed increasingly a method wherein a hydrogen peroxide producing enzyme, for example, an oxidase is used so as to produce H.sub.2 O.sub.2 corresponding to the desired component, the produced H.sub.2 O.sub.2 is led to a color forming system by using peroxidase and an oxidizable color producing reagent which is a chromogen, and the color produced is determined colorimetrically to obtain the amount of the desired component. For example, H.sub.2 O.sub.2 produced by a combination of cholesterol-cholesterol oxidase, triglyceride-lipoprotein lipase-glycerol oxidase, or uric acid-uricase, is led to a color forming system by using peroxidase (POD) and an oxidizable color producing reagent, and absorbance of the color produced is measured to determined the amount of the desired component. Typical examples of the oxidizable color producing reagents which are chromogens used in this method are combined reagents of 4aminoantipyrine and a phenolic compound or an N,N-disubstituted aniline series compound, combined reagents of 3-methylbenzothiazolinone hydrozone (MBTH) and an aniline series compound, 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), triphenylmethane series leuco dyes, benzidine derivatives, o-tolidine derivatives, triallylimidazole derivatives, o-phenylenediamine, etc. But almost all the oxidizable color producing reagents have a wavelength of color formed at 600 nm or less and are readily influenced by serum components such as bilirubin, hemoglobin, etc. (in the case of measuring urine components, these are readily influenced by colored matters in urine). Further, chromogens of the oxidizable color producing reagents are low in stability except for the combined reagents of 4-aminoantipyrine and a part of the triphenylmethane series leuco dyes.
On the other hand, there are proposed diphenylamine derivatives which are dye precursors (leuco dyes) and are chromogens relatively good in stability and having a wavelength of color formed at a relatively longer wavelength side in European patent publications Nos. 38205, 124287 and 45220. These diphenylamine derivatives have the wavelength of color formed at a relative longer wavelength side such as 700 nm or more and are relatively high in sensitivity, but are insufficient in chromogen stability and stability of the color formed and poor in solubility in water.
In order to overcome the disadvantages of the diphenylamine derivatives, surface active agents and/or organic solvents are generally used as a dissolution auxiliary so as to make the chromogen soluble and to prepare a color producing reagent solution. But when enzymes such as glycerophosphate oxidase, lipopretein lipase, cholesterol oxidase, cholesterol esterase, phospholipase D, etc. are present in the measuring system, there are many problems, for example, in that these enzymes are relatively easily deactivated by surface active agents and require limited kinds of or concentrations of surface active agents. Therefore, such a process is not preferable. On the other hand, when these diphenylamine derivatives are used as a chromogen in a color producing reagent solution contained in commercially available clinical examination reagents, they have to be contained in socalled lyophilized products, since they have no stability in an aqueous solution for a long period of time. But since the chromogen should be dissolved in a starting liquid of the lyophilized products in amounts 10 to 100 times as much as the concentration usually used, a special technique is required for preparing the starting liquid. Thus, there are many problems in practical use.